The present invention relates to photodetectors, and, in particular, relates to photodetectors that operate in a range of about 0.2 microns to 1.8 microns.
One major problem with present photodetectors is that they lack a broad range of light sensitivity. For example, a p-i-n photodiode is sensitive to photons with energies near the band gap energy. If hv is less than E.sub.g, the photons will not be absorbed; on the other hand, if the photons are much more energetic than E.sub.g, they will be absorbed very near the surface, where the recombination rate is high. Therefore, it is necessary to choose a photodiode which is sensitive to a particular region of the spectrum. This generally means that semiconductor diodes such as GaAs, Si, and Ge respond best to band gap light. For example, a silicon diode responds to a range from about 0.3 to 1.0 .mu.m. Germanium photodetectors have a range of about 0.6 to 1.9 .mu.m.
If very low level optical signals of a desired wavelength are to be detected, the photodetector can be operated in the avalanche mode.
Although present apparatus can measure light intensity over a limited range, a much broader range is desired.